Orthodontics is a field of dentistry associated with the professional supervision, guidance and correction of malpositioned teeth. The benefits of orthodontic treatment include attaining and maintaining a proper bite function, enhancing facial aesthetics, and improving dental hygiene. To achieve these goals, the orthodontic professional often makes use of corrective appliances that engage to the patient's teeth and apply gentle therapeutic forces to move the teeth toward proper positions.
One common type of treatment uses tiny slotted appliances called orthodontic brackets, which are adhesively attached to either the front or back surfaces of the teeth. To begin treatment, a resilient arch-shape wire (“archwire”) is received into the slot of each bracket. The ends of the archwire are generally captured in appliances called molar tubes, which are affixed to the patient's molar teeth. As the archwire slowly returns to its original shape, it acts as a track that guides the movement of teeth toward desired positions. The brackets, tubes, and archwire are collectively known as “braces.”
The procedure used to engage and activate the archwire on the orthodontic bracket is known as ligation. Traditional brackets are ligated to the archwire with the help of one or more pairs of opposing tiewings, or cleat-like projections on the bracket body. The archwire is placed in the archwire slot and generally a tiny elastomeric “O”-ring ligature, or alternatively metal ligature wire, is tightened over the archwire and under the undercut portions of tiewings located on opposite sides of the archwire slot. The ligature thus secures the archwire within the archwire slot of each bracket and provides a precise mechanical coupling between these bodies.
Ligatures have numerous drawbacks. For example, elastomeric ligatures have a tendency to lose their elasticity over time, resulting in inconsistent archwire sliding mechanics. While these ligatures can be made translucent for aesthetic treatment, they also tend to easily stain. Ligation using a ligature wire, on the other hand, can be quite cumbersome and time-consuming. Being made of metal, ligature wire is also generally considered non-aesthetic.
Self-ligating brackets present a solution to the above problems. These appliances generally use a clip, spring member, door, shutter, bail, or other ligation mechanism built into the bracket itself to retain the archwire in the slot, thereby obviating use of a separate ligature. Several advantages can derive from the use of self-ligating brackets. For example, these appliances can decrease friction between the archwire and the bracket compared with brackets ligated with elastomeric ligatures, potentially providing faster leveling and aligning of teeth in early stages of treatment. Depending on the ligation mechanism, these appliances can also simplify the installation and removal of an archwire, significantly reducing chair time for the treating professional. Finally, self-ligating brackets can also provide better hygiene than conventional brackets, which use elastomeric ligatures and ligature wires that can trap food and plaque.